cache collect_trait_impl_trait_tys

compiler/rustc_middle/src/arena.rs

@@ -102,7 +102,7 @@ macro_rules! arena_types {
 
             [] dep_kind: rustc_middle::dep_graph::DepKindStruct<'tcx>,
 
-            [] trait_impl_trait_tys: rustc_data_structures::fx::FxHashMap<rustc_hir::def_id::DefId, rustc_middle::ty::Ty<'tcx>>,
+            [decode] trait_impl_trait_tys: rustc_data_structures::fx::FxHashMap<rustc_hir::def_id::DefId, rustc_middle::ty::Ty<'tcx>>,
         ]);
     )
 }

compiler/rustc_middle/src/query/mod.rs

@@ -164,7 +164,8 @@ rustc_queries! {
     query collect_trait_impl_trait_tys(key: DefId)
         -> Result<&'tcx FxHashMap<DefId, Ty<'tcx>>, ErrorGuaranteed>
     {
-        desc { "better description please" }
+        desc { "compare an impl and trait method signature, inferring any hidden `impl Trait` types in the process" }
+        cache_on_disk_if { key.is_local() }
         separate_provide_extern
     }
 

compiler/rustc_query_impl/src/on_disk_cache.rs

@@ -798,6 +798,12 @@ impl<'a, 'tcx> Decodable<CacheDecoder<'a, 'tcx>> for &'tcx FxHashSet<LocalDefId>
     }
 }
 
+impl<'a, 'tcx> Decodable<CacheDecoder<'a, 'tcx>> for &'tcx FxHashMap<DefId, Ty<'tcx>> {
+    fn decode(d: &mut CacheDecoder<'a, 'tcx>) -> Self {
+        RefDecodable::decode(d)
+    }
+}
+
 impl<'a, 'tcx> Decodable<CacheDecoder<'a, 'tcx>>
     for &'tcx IndexVec<mir::Promoted, mir::Body<'tcx>>
 {